1. Field of the Invention
The invention relates to the field of full water blown polyurethane compositions and processes. More particularly, it relates to processes and compositions for preparing full water blown rigid foams that exhibit good foam stability and adhesion even at low densities.
2. Background of the Art
Processes for preparing full water blown rigid polyurethane compositions have been part of a well-established technology that has seen significant commercial success. Such compositions are frequently used in the cold chain industry, to ensure narrow temperature control for products such as pharmaceuticals, vaccines, and food throughout their storage and shipping cycles. However, those involved in relevant industries have long recognized certain problems that often limit application. In particular, full water blown polyurethanes suffer from a relatively high k-factor, due the presence of carbon dioxide inside the foam cells, thereby limiting applications requiring good insulation capability. Furthermore, the final density of the foams is often higher than desired.
The processes to prepare these compositions also may experience difficulties. For example, the foams may be brittle, or suffer from poor adhesion to substrates due to the relatively high urea concentration that often forms on the surface of these foams. The foams may also be dimensionally unstable, due to a relatively high diffusion coefficient of the carbon dioxide through the cell walls, and demold may be poor due to the relatively high exothermic nature of the water-blown reactions. Therefore researchers in the area acknowledge that it is difficult to prepare foams with acceptable mechanical properties wherein the formulated polyol's water content is significantly above about 4 percent by weight (wt %), based on the weight of the formulated polyol as a whole. Thus, there remains a need in the art for new processes and compositions with the ability to utilize high levels of water as the blowing agent to avoid or reduce the problems mentioned above.